I question why you wanted air bags installed. I bet your 3/4 ton suspension was perfectly happy to connect to the pin weight without air bags. Take them off, the back of the truck will drop a couple of inches.
I had bags on my one ton and when they finally fell apart and I cut them out I could connect up to my boat trailer without putting a lift board under the front loading crank up wheel on the trailer.
Bags are generally used when carrying a heavy load, more like a camper than a light fifth wheel, and they are not designed to be pumped up and lift the camper up, they are designed to correct side to side sagging. Try dropping bag pressure down to 15 (or the minimum they are supposed to have), but even still you might have to remove them entirely. Certainly something is very wrong as the fifth wheel should ride level.